radioactive lcd

[digibloke]

Check out the radioactive symbol on the back of this NS lcd. (hope it's ok to post your pics bastibeppi - if not just say and I'll remove the post).

http://cgi.ebay.com/Super-Teil-Digitale ... dZViewItem

Apparently they used 3H-Thymidine to light the display and if the modules had to be opened for repair then they had to be sent back to the factory for safety reasons

I guess that they used so little that it was harmless - but a watch with a radioactive waste symbol on it has got to be cool eh?

[fronzelneekburm]

I also have a tritium lit LCD watch, what was the model called? Was it "Tr-Lite" or so? I gotta look when I'm back home. Unfortunately the effect is gone over the years, halflife for tritium is less than 10 years I think, so after 30 years you dont see it glowing any more, not even in total darkness.

The radioactive symbol on the back is indeed unique, I am sure my tritium lit watch does not have such markings.

[lars]

Hey, I had one of those back in 1979!! I was really ticked off too. It quit on me so I took it into the Sears store where it was origianlly bought for service. They serviced it by sending me a new one. The problem? The new one wasn't tritium backlit - had the crappy little incadescent bulb in it. I still have that one.

BTW, my "recent" Luminox does say 3H on the back but does not have the radioactive symbol.

BTW#2, the symbol does not mean radioactive waste - just radioactive. Why is it that the synonym for chemical is so often "hazarouds chemical waste"???

Paul

P.S. Yes, I'm a chemist.

[cleversod]

hey, I used to have one that was "tritium lit" , was quite a nice watch, was just about the first one that would actually stay on my wrist and not break.
As I remember, forgive me if I'm wrong, but I think Tritium was based on a hydrogen isotope, otherwise known as "heavy water"??
had a strange, eerie, but briight glow, no need to press a button, it just glowed all the time !
any of these left?
ta
John

[fronzelneekburm]

Tritium is indeed a hydrogen isotope. H3 to be exact. :wink:

Due to the (weak) radioactivity it was always discussed for use in consumer products. In several countries products containing radioactive materials are banned. Here in Germany the situation is not 100% clean. For example tritium torches are sold only to government, police and such. The small keyrings with tritium vials have however appeared on the german market, claimed to be illegal but none actions have been done to prevent further spreading.

The general concerns are less for the consumer himself - the radioactivity is not very strong while properly built into the watch, but the disposal is often regarded as a problem. As all consumer product, watches tend to be "thrown away" when broken or batteries died. While this for sure does not apply to collectors like us this is how many normal consumers treat watches, especially "cheap" ones. If a product becomes a "hit" and millions of tritium loaded products land on the trash dump it could arrise to a problem.


Here's some beautifull examples of Tritium usage in watches today:

http://ballwatchusa.com/technology/trit ... nology.htm

http://ballwatchusa.com/collection/Trai ... JNight.htm


Unfortunately there are no digital watches of today that are using tritium light sources.

[rewolf]

I have a 1976 Tritium lit Fairchild LCD. It still glows a bit in the dark, but not enough to read it
Tritium has a half-time of 12.3 years, so after 30 years it's at 18% of its original level.

[Synchroserious]

My father wrote in 1977 "These are Phosphorous lined glass tubes with radio active tritium gas.The glow they give off fades to half in five years"

I think there is no exact standard but you must be refering to the absolute best tritium gas backlight specs given, does it specify or claim the 12.3 years on the manual for the watch? Not saying you are wrong but I am currious of where the 12.3 year figure for half life came from.

[retroleds]

Just had to chime in....you guys may both have the right numbers, but you are comparing "apples & oranges". Radioaactive level and light brightness won't necessarily change at the same rate. Consider a common incadescent lightbulb on a dimmer - once the voltage gets down to around half, the bulb will cease to glow. Flourescent bulbs won't glow at all if their voltage drops just 10%. 1/2 strength tritium may not be able to excite the phosphorus at all.

[Synchroserious]

The strength or radioactive life left is not what i thought we were talking about.Glow life is all that really matters,unless there is a health concern,which seems to be over in watch use anyway.The High Quality Ball watch that fronz posted I am sure has a better tech way of doing it.For one 10-50% glow is all you need on hands in the dark.You would get more usefullness of low glow in an analog aplication even using the old technology it seems.


OK I see now where I took Rewolfs post wrong the first time I looked at it He did mean 18 % strength level,the first sentence about glow threw me off. I don't know much about it really just chipping in,thanks ED. Sorry Rewolf

[retroleds]

You are right Howard - glow life is all that really matters. 1/2 life, 1/4 life..as long as it's working. :) But it is interesting to ponder how long the stuff might be "hazardous". Beats the hell out of the stuff in nuclear bombs.

[rewolf]

I think there is no exact standard but you must be refering to the absolute best tritium gas backlight specs given, does it specify or claim the 12.3 years on the manual for the watch? Not saying you are wrong but I am currious of where the 12.3 year figure for half life came from.

Half life 12.3yrs is an inherent property of the element Tritium, click here.
But, as retroleds pointed out, the actual glow might not correlate linearly with radioactivity. Plus: phospors age (as you can see in an old picture tube or old videorecorders with VFD display). That makes it decay even faster :(

[lars]

Hang on, physics is physics. Therfore, the light output from the excited phosphors will be proportional to the decay of the tritium.

T -> He+ + e- + ve

It's this "beta particle" or electron carrying away the energy that strikes the phosphor to generate visible light. The decay rate is a property of the element and can not be otherwise influenced. If it didn't decay, there would be no glow.

This means if there is half the tritium left after 12.3 years, there will be half as many decays per unit time and half of the light intensity will be generated. After a further 12.3 years, one quarter will be left, one quarter of the light intensity, etc. Linear it's not but directly proportional to the amount of remaining tritium it is.

That said, as already pointed out, the phosphors may decay too so the light output may indeed drop further - that's however not very likely in my mind. In general, the inorganic compounds that I know to have been used for this purpose are inorganic and quite stable.

Paul

[rewolf]

That said, as already pointed out, the phosphors may decay too so the light output may indeed drop further - that's however not very likely in my mind. In general, the inorganic compounds that I know to have been used for this purpose are inorganic and quite stable.

Hm, any phosphor that I know ages: TV screens (CRT and plasma type), VFD display, flourescent tubes. But perhaps the phosphor used for tritium backlichts is different - I don't know.
The light output is proportional to the decay rate if there are no secondary effects or activation thresholds involved. I don't know either...

[635 nm.]

I remember I bought one from a JS&A catalog and the thing was bright enough to read a book by, it was the perfect ice breaker the disco, you could see it glowing under your polyester print shirt sleeves. I wonder why no one has made one in modern times. Maybe it has to do with the amount of tritium you can use in one device. The Luminox analog watches from the early 1990s were three times the brightness of the new ones. The exit signs on older airliners also used a tritium light source to stay lit no matter what.
Richard.

[retroleds]

REACTOR brand watches has a new "Never Dark" system in their watches, which uses a super bright phosphourescent material in combination of Tritium. Seven years of legibility in total darkness. http://www.reactorwatch.com/nvd.html

[rewolf]

Peter Doensen covers this topic in his book here; related photo

[TheFordGuy]

I'd love to find a vintage Texas Instruments LCD with this tritium backlighting like the one my dad had back in the late '70s. It was a very stylish watch, but just a basic 5-function module with no alarm or anything. Time, date, and seconds was all it did.

I've seen several that vaguely resemble it, but this exact one might be tough to come across.

It's also a bummer that if I did find it, it most likely wouldn't glow anymore. That was absolutely fascinating to me when I first saw that new technology back in the day, and I'm sure it would attract a little attention now that it's more or less obsolete in digital watches.